Don't process min-slaves-to-write for slaves.

Replication is totally broken when a slave has this option, since it
stops accepting updates from masters.

This fixes issue #1434.

src/redis.c

@@ -2037,7 +2037,8 @@ int processCommand(redisClient *c) {
 
     /* Don't accept write commands if there are not enough good slaves and
      * user configured the min-slaves-to-write option. */
-    if (server.repl_min_slaves_to_write &&
+    if (server.masterhost == NULL &&
+        server.repl_min_slaves_to_write &&
         server.repl_min_slaves_max_lag &&
         c->cmd->flags & REDIS_CMD_WRITE &&
         server.repl_good_slaves_count < server.repl_min_slaves_to_write)